1. Field of the Invention
The present invention relates to an internal combustion engine and more particularly to a method well adaptable for measuring an injection amount from an injection pump which is used for fuel oil injection into a Diesel engine and an apparatus for executing it, which are used for adjusting and inspecting the injection pump in its manufacturing factories, for example.
2. Description of the Prior Art
In this type of the injection amount measuring method, fuel oil is injected into an injection chamber through a nozzle of an injection pump to be measured. By the fuel oil injected, a piston is pushed to displace. A displacement of the piston is converted into an electrical signal by a displacement detector mainly including a differential transformer. The electrical signal is inputted into an arithmetic unit. The arithmetic unit is arranged to set the electrical signal from the displacement detector before the injecting of the injection pump at zero as a reference, and then an electrical signal from the displacement detector after the injecting is converted into an injection amount of fuel oil. Finally, the injection amount of fuel oil is visually displayed.
According to the present inventor's study of the prior art measuring method, it has been found that for the following reason the injection amount measurement with high accuracy is unfeasible by the prior art method. In the prior art measuring method, a difference between the pressure within the injection chamber before the injecting and the pressure after the injecting is too large (e.g. 7 Kg/cm.sup.2). Therefore, an increase of the volume resulting from the injecting in the injection chamber is reduced by the amount corresponding to an amount of a compressed volume as a result of the pressure difference. Therefore, the prior art method measures the injection amount smaller than an actual injection amount by the reduced amount of the volume increase. Particularly within the injection chamber, a small amount of gas as well as the fuel oil is present, the former being mixed into the fuel oil. Since a volume of the gas is inversely proportional to pressure, the compressed volume as a result of the pressure increase is also large. For example, when the volume in the injection chamber is 400 mm.sup.3, it reaches even 2 to 6 mm.sup.3 of the compressed volumes of the gas and the fuel oil. The prior art method measures the injection amount reduced by the compressed volume, thus making it difficult to measure the injection amount with high accuracy.